The present invention relates to a novel device for the heat treatment of divided material and particularly of powdery or granular material.
Heat treatment by means of microwaves (M.O.) or ultrahigh frequency waves (UHF) having wavelengths between about 300 Megahertz and about 30 Gigahertz is becoming at present more and more widespread, particularly because of the ready availability of this energy, its good propagation in various atmospheres, its good regulation and its satisfactory control. The homogeneous heating throughout the whole of the mass of the product treated which it provides has furthermore allowed numerous applications of this form of energy, not only in the domestic but also in industrial fields. There existed however an important drawback, at least insofar as the industrial applications of UHF radiation are concerned: although the discontinuous or batch treatment of the different products and materials is as a whole satisfactory and presents no great problem, the same cannot be said for the continuous treatment of large quantities of materials, and particularly of materials in the divided state, such as grains, powders or similar. In fact, for this mass heat treatment to be economically profitable, very large quantities of material must be treated, and this without loss of energy, and robust and simple installations must also be available. None of the installations of the prior art complies with these basic requirements.
The use of multimode resonator cavities is excluded: on the one hand there is not enough energy density concentration and, on the other hand, very large volumes would have to be constructed, something which is difficult to achieve and economically unprofitable.
It is also economically unprofitable to provide a succession of resonator cavities connected to each other (as for example the construction of an enclosure forming a "tunnel" passing through the resonator cavities, as is recommended in French Pat. No. 2,428,369): there also occur considerable energy leaks due to the input and output system for the material.
The use of monomode and multimode wave-guides has also been recommended using not stationary waves but progressive waves. Thus coaxial devices have been constructed in which the materials to be treated are inside the wave-guide or else devices with emitting antennae, in which the materials to be treated receive the M.O. radiations.
Besides the fact that, in the devices of the prior art, the flow rate of the materials to be treated is limited, even with the installation of conveyor belts, there occur furthermore high energy losses for the material to be treated thus conveyed so the material is not in the maximum energy concentration zone. Numerous other attempts at constructing continuous M.O. energy applicators have been described for example:
1. A device using an endless screw (French Pat. No. 2,337,734), PA0 2. A device using a rotating plate (U.S. Pat. No. 3,676,058), and still others.
But in all cases, the same handicap exists: insufficient flow rate, a too high loss in energy, prohibitive cost of installation.